SIC 3451

This category includes establishments primarily engaged in manufacturing automatic or hand screw machine products from rod, bar, or tube stock of metal, fiber, plastics, or other material. The products of this industry consist of a wide variety of unassembled parts and are usually manufactured on a job or order basis. Establishments included in this industry may perform assembly of some parts manufactured in the same establishment, but establishments primarily engaged in producing assembled components are classified according to the nature of the components. Establishments primarily engaged in manufacturing standard bolts, nuts, rivets, screws, and other industrial fasteners on headers, threaders, and nutforming machines are classified in SIC 3452: Bolts, Nuts, Screws, Rivets, and Washers.

NAICS Code(s)

332721 (Precision Tuned Product Manufacturing)

Industry Snapshot

According to the Precision Machine Products Association (formerly the National Screw Machine Products Association), more than 1,600 companies employed more than 56,000 highly skilled workers throughout North America in the late 1990s. These companies utilized traditional methods combined with cutting-edge technologies, such as automatic screw machines, computer-controlled (CNC) single- and multiple-spindle lathes and CNC turning and machining centers, to manufacture billions of component parts to precise specifications. This industry machined components used in a multitude of end products, including anti-lock brakes, transmissions, fuel injection systems, car airbags, computer hard drives, video recording equipment, medical diagnostic equipment, and power tools, to name just a few.

The screw machine products industry is defined more by the process of manufacture than by any specific product. Although screw machine products manufacturers produce a wide variety of products for many types of industries, they all use a variation on the screw machine—a large, usually cam-driven piece of machinery that allows roughly cylindrical material to be subjected to a variety of tooling and machining operations as the material is turned about its axis. Screw machines may have as many as eight spindles that act upon the part being machined, and are able to produce highly precise parts quickly. The screw machine, by ensuring the interchangeability of manufactured parts, was a major contributor to the development of modern manufacturing and assembly processes.

Screw machine products manufacturers are located primarily in the industrialized sectors of the Northeast and Midwest and near aerospace manufacturers in the West. The industry is dominated by smaller companies employing fewer than 50 workers, most of whom are highly skilled machinists. Many of the shops are privately owned, and most are located close to the industries to which they supply parts. In addition, many larger companies that use screw machine products manufacture those products in-house. The automotive industry is the major purchaser of screw machine products and accounts for 30 percent of the industry's shipments, which totaled $8.54 billion in 2000.

Organization and Structure

The vast majority of screw machine products are manufactured on a job or order basis. The purchaser of a product provides the manufacturer with a precise description of the part desired, and the manufacturer then sets up its machines to produce that part. Part runs may call for the manufacture of as few as a hundred or as many as a million parts, requiring a single screw machine or a shop full of machines to produce the part on time. Because of the nature of their business, screw machine products manufacturers rely on the flexibility of their equipment and employees to accommodate the different needs of the various screw machine products purchasers.

Three types of screw machines are used by manufacturers: swiss, single-spindle, and multiple-spindle machines. Using these machines, a machinist may perform up to 32 different types of cutting and forming operations. Fred W. Lewis, discussing the screw machine products industry in the Handbook of Product Design for Manufacturing , stated, "The amount of work done is limited only by the number of tool positions available and the tool layout engineer's ingenuity." The tool layout engineer designs the cams that control the various machining operations and sets up the machine, which is then capable of producing millions of identical pieces. Many manufacturers are turning to computer-controlled rather than cam-controlled operations, because of the longer set-up time required for cam-driven machines and the level of expertise required to operate them. Computer-controlled screw machines, however, are not necessarily more productive than cam-driven machines.

The flexibility inherent in both machine and machinist allows screw machine products manufacturers to produce parts for many types of industries. While larger manufacturers have diversified their production, smaller companies have tended toward specialization and may produce as much as 80 percent of their total output for one company. This degree of commitment means small manufacturers experience whatever economic downturns or upturns their customer experiences. The actual screw machines account for the major capital expenditures of manufacturers in this industry. The screw machine is a remarkably durable piece of machinery, however; it can be rebuilt and overhauled, and computer controls can be added to enhance the machine's flexibility, thus spreading capital outlay out over a long period of time.

The screw machine products industry is characterized by a high degree of structural stability: the machinery it uses, the processes involved in manufacture, and the kinds of products it produces have remained essentially the same for nearly 100 years. Many manufacturers use screw machines that are decades old. Most employees learn their trade through hands-on training or a form of apprenticeship, though workers are increasingly receiving training in vocational education programs. Thus, the screw machine operator of two generations ago would recognize many of the operations being conducted in today's shop, though the veteran workers might be surprised to see young operators who had not gone through an apprenticeship programming computer-controlled screw machines to work on plastics and fibers as well as metals.

Background and Development

Although the first machine-cut screws were produced in 1800, at the dawn of the first industrial age, the concept of a screw dates back as far the third century B.C., when the Greek mathematician Archimedes designed a water-powered, screw-driven system to lift water. Much later, in the mid-1400s, Leonardo da Vinci drew plans for a screw-cutting lathe. But it was Henry Maudslay, an English mechanic, who in 1800 first cut a piece of lead on a lathe into the helical pattern we know as a screw. Early screw manufacturers were hampered by the lack of any standards for measuring their products or ensuring their uniformity. Thus, each producer made a different size and pitch of screw, making it very difficult to replace parts when needed.

The early manufacture of machined metal parts in the United States occurred primarily in the increasingly industrialized Northeast states, where small shops produced parts for the machines that would drive American economic growth. Such shops used belt-driven lathes that were powered by water or, occasionally, an ox tied to a treadmill outside the factory. It was not until the middle of the nineteenth century, however, that a small group of machinists centered around Windsor, Vermont, created the machine tools that preceded today's screw machines. Out of this innovative environment of skilled inventors and machinists, which included pioneers Francis A. Pratt, Richard Lawrence, and James Hartness came Christopher Spencer, who in 1873 created the Hartford Automatic Screw Machine.

According to Donald E. Wood, editor of Automatic Machining and author of From Archimedes to Automation: The History of the Screw Machine , Spencer's automatic screw machine was "the prototype for all single-spindle machines in use today." This machine was manufactured by the Hartford Machine Screw Co., which is the oldest continuing screw product manufacturer in the country. Soon Pratt & Whitney Co. of Hartford, Connecticut, and Brown & Sharpe Manufacturing Co. of Providence, Rhode Island, began manufacturing screw machines that were famed for their precision and accuracy. The creation of precision screw machines contributed greatly to the development of modern manufacturing, as screw machines made products for the growing automotive industry and other developing industries. According to Wood, "The mass production of consumer goods, and its parallel problem, precise interchange ability of goods components, came only after machine tools had been devised which could make products alike in a rapid manner, and standardization of measurement had been established."

Although the screw machine was initially designed to produce threaded fasteners, users of the machine soon recognized that it was capable of producing a vast number of products. In fact, standardized screw thread manufacturers soon turned to a different process, called cold-heading, and this industry is now classified as SIC 3452: Bolts, Nuts, Screws, Rivets, and Washers. Because the screw machine could create any roughly cylindrical, symmetrical piece of stock, it soon was used to manufacture gears, pulleys, push rods, rollers, and other products. By 1960 more than 1,500 screw machine product manufacturers employed more than 30,000 workers and operated over 40,000 screw machines to produce nearly $1 billion in annual sales of special component parts.

Current Conditions

The value of shipments for the industry fluctuated in the late 1990s, growing from $8.3 billion in 1997 to $8.6 billion in 1998, before falling to $8.2 billion in 1999. Shipments increased again in 2000, reaching $8.5 billion. The cost of materials remained relatively stable during this period, hovering around $2.8 billion.

Industry-wide sales totaled approximately $5.4 billion in the late 1990s, according to the most recent statistics available from the Precision Machine Products Association. Companies averaged sales of $3.3 million, and the average growth rate of the industry, adjusted for inflation, was projected to be 3 to 5 percent into the early 2000s.

Industry Leaders

Detroit-based United Technologies Automotive Inc. Engineered Systems Div. led the industry with $975 million in 1997 sales, according to the most recent information available on Infotrac. Cerro Metal Products Co. of Bellefonte, Pennsylvania, generated $250 million in 1997 sales, and the Kurt Manufacturing Co. garnered $108 million in 1997 sales. The U.S. Environmental Protection Agency's Region 5 office slapped a $20,000 fine on Kurt in 1997 for not disposing of polychlorinated biphenyls (PCBs) on time.


Manufacturers of screw machine products have traditionally employed a highly skilled work force, although the aging of highly trained employees and the availability of more accessible computer-controlled machines suggests that the work force of the future will be younger and somewhat less skilled. Because learning to set up a camcontrolled screw machine takes years of training, finding qualified employees has been one of the industry's biggest problems. Operators traditionally learned the intricacies of setting up a machine through an apprenticeship; but vocational training programs and on-the-job training have now supplanted formal apprenticeships. In addition, the Precision Machine Products Association, located near Cleveland, Ohio, provides training manuals, videos, and seminars for its members. The industry's move to greater computerization is driven less by the inherent technical benefits of computer control than by the greater ease of training that computers allow.

Most employees in the screw machine products industry are machinists of some sort. Because manufacturers are provided with design specifications for their products, they employ no designers. Manufacturing engineers specify the machining operations and cams required to produce the job based on the design they are given, and machinists set up the machines and supervise their operation. In many smaller firms, the principal owner is also the head engineer.

Total employment for the industry remained fairly constant from 1984 to 1988. Employment levels reached 45,900 in 1989 but dropped to 40,600 in 1991. Employment later rebounded, and in 2000 the industry employed 77,860 people. Production workers' employment levels followed a similar pattern to total employment levels, with a low of 32,300 in 1991 increasing to 62,099 by 2000.

In the late 1990s, approximately 2,745 establishments in the United States manufactured screw machine products. Only 40 percent of these establishments employed more than 20 employees. Average wages for this industry have steadily increased from $7.72 per hour in 1982. However, the average pay of $11.25 per hour in 1994 was slightly lower than the national standard of $12.09 for all manufacturing industries. By 2000 the average hourly wage for production workers in the industry was $15.16.

Further Reading

Darnay, Arsen J., ed. Manufacturing USA: Industry Analysis, Statistics, and Leading Companies , 5th ed. Farmington Hills, MI: Gale Group, 1996.

Infotrac Company Profiles. 1 January 2000. Available from .

"Kurt Manufacturing to pay $20,000 fine." American Metal Market , 4 March 1997.

Lewis, Fred W. "Screw Machine Products." Handbook of Product Design for Manufacturing: A Practical Guide to Low-Cost Production. New York: McGraw-Hill, 1986.

Precision Machine Products Association. 18 January 2000. Available from .

United States Census Bureau. "Statistics for Industries and Industry Groups: 2000." Annual Survey of Manufacturers. February 2002. Available from .

United States Census Bureau. Survey of Manufacturers , 10 February 2000. Available from .

Ward's Business Directory of U.S. Private and Public Companies. Farmington Hills, MI: Gale Group, 1997.

Wood, Donald E. From Archimedes to Automation: The History of the Screw Machine. Brecksville, OH: National Screw Machine Products Association.

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